This invention relates to image encoding and decoding techniques and more particularly to motion encoding and decoding.
Several existing methods enable a portion of a current image to be encoded relative to other portions of previously decoded images, according to a so-called “INTER” encoding mode. The current image portion is represented by luminance and chrominance information and information relating to the motion between this current image portion and a reference image portion. This enables the temporal correlations between the images to be exploited.
The motion information includes one or more components, e.g., like a translational motion vector, rotation, a pixel component and a subpixel component. Encoding generally includes the determination of information for reconstructing the motion components. For example, a motion vector is predicted and the information for the reconstruction comprises the prediction function identifier used as well as a remainder corresponding to the difference between the prediction and the original motion vector.
The reconstruction information likewise includes other information of various types which enable the components of the motion to be obtained from the decoder. For example, this information is called related or “side information” and consolidates size parameters, function identifiers to be used or others.
This reconstruction information is transmitted to the decoder.
The decoder reconstructs the various components of the estimated motion, i.e., applies the reverse prediction, and combines the result with the remainder and the related information. The decoder next applies the motion components with the reference image portion and combines the result with the luminance and chrominance information in order to obtain the decoded image.
The motion components are information the size of which increases with the resolution of the images, and the information for reconstructing these components occupies a significant portion of the bandwidth.
This poses problems, particularly in environments where the bandwidth is limited, such as wireless environments.